1. Field of the Invention
The present invention relates to a yoke-type lifting magnet device and, more particularly, relates to a movable yoke-type lifting magnet device.
2. Description of the Related Art
A yoke-type lifting magnet device is described in Japanese Utility Model Publication SHO No. 51-126570. The device has a pair of yokes mechanically and fixedly coupled to a core and each yoke includes a plurality of slidable pieces which are mechanically coupled to the yoke so as to slide vertically relative to the yoke when magnetic flux is not induced therein. Such a mechanical coupling for vertical movement needs a vertically extending hole formed in one member and a rod fixed to the other member penetrating the hole and therefore, the vertical movement of the slidable piece is limited by the length of the hole. As a result, the device can not freely follow the contour of a workpiece to be lifted.
To enable a yoke to freely follow the contour of a workpiece it might be effective to couple the yoke magnetically with the core, though such a magnetic coupling may cause slippage between the yoke and the core.